To isolate and purify specific hormone receptors in particular receptor tissues; to map function of the receptor against activation of adenylate cyclase; to determine the nature of the link between generation of cyclic 3',5'-AMP and solute transport in particular cell systems. Beta-adrenergic receptors have been identified using radioiodinated hydroxybenzylpindolol (1-(1-para-hydroxyphenyl-2-methyl-propylamino)-3-(4-indolyloxy)-2-propanol), a high-affinity beta-blocker. This compound binds specifically to beta-receptor sites on cell membranes. Kinetic and equilibrium studies identified a single class of high affinity (2-4 x 10 to the 10th power M-1) receptor sites on turkey erythrocyte membranes, 200-400 sites per cell. A series of beta-adrenergic agonists and inhibitors compete for this binding site with affinities paralleling biological effectiveness as activators or inhibitors of catecholamine-stimulated adenylate cyclase. The stereospecificity and the correspondence between affinity for site and biological effectiveness indicate that binding of iodohydroxybenzylpindolol validly reflects interaction with beta-adrenergic receptors in several cell systems.